Multistage gas sampling trap and detection of sulfurous species contaminant

ABSTRACT

A gas sampling trap includes a first stage and a second stage. The first stage includes a metal salt that reacts with sulfurous species to produce acidic gas. The second stage configured to receive the acidic gas produced in the first stage. An adsorbent substrate in the second stage adsorbs the acidic gas. A method of sampling a gas includes directing gas onto a metal stage within a first stage to produce acidic gas, directing the acidic gas into the second stage, and adsorbing the acidic gas in the second stage with an adsorbent substrate. A method of detecting a concentration of sulfurous species in a gas includes sampling the gas with a sampling trap, desorbing adsorbed acidic gas from an adsorbent substrate of the sampling trap with a solvent, and testing the solvent with ion chromatography.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119 of U.S. ProvisionalPatent Application No. 63/185,812 filed May 7, 2021, the disclosure ofwhich is hereby incorporated herein by reference in its entirety.

FIELD

This disclosure relates to sampling of gas for contaminants. Inparticular, this disclosure relates to sampling traps used in samplinggas to detect for sulfurous contaminants.

BACKGROUND

Gas sampling can be used in chemical processing, semiconductormanufacturing, gas distribution, and the like to detect for contaminantin a stream of gas. In particular, gas sampling can be used to detectfor airborne micro-contaminants in a stream of gas. Examples of gasstreams that may be sampled can include, but are not limited to filteredair (e.g., clean dry air, and the like), ambient air, purified nitrogen,and purified hydrogen. Canister sampling fills a sampling canister witha sample of gas. Gas sampling traps can be configured to contain justthe particular compound(s) of interest within the sampling trap. Thecontents of a sample canister or a gas sampling trap can be used todetermine the concentration of the contaminant in the sampled gas.

BRIEF SUMMARY

In an embodiment, a gas sampling trap includes a first stage and asecond stage. The first stage includes an inlet for receiving a flow ofgas and a metal salt. The metal salt is configured to react withsulfurous species contained in the gas to produce an acidic gas. Thesecond stage is fluidly connected to the first stage such that theacidic gas produced in the first stage flows into the second stage. Thesecond stage includes an adsorbent substrate that is configured toadsorb the acidic gas flowing through the second stage.

In an embodiment, the reaction of the metal salt with the sulfurousspecies produces the acidic gas and a metallic sulfur compound.

In an embodiment, the metal salt includes one or more of silver nitrate,zinc acetate, and copper acetate.

In an embodiment, the sulfurous species includes one or more of hydrogensulfide, dimethyl sulfide, dimethyl disulfide, methyl mercaptan, and amethyl sulfide compound.

In an embodiment, the acidic gas includes one or more of nitric acid andacetic acid.

In an embodiment, the adsorbent substrate adsorbs the acidic gas suchthat the acidic gas remains stably adsorbed to the adsorbent substrateafter a period of 10 days.

In an embodiment, the adsorbent substrate is a porous polymer membranethat adsorbs the acidic gas such that the acidic gas is trapped withinthe porous polymer membrane.

In an embodiment, the gas contains less than 400 parts per billion ofthe sulfurous species.

In an embodiment, the gas is one of filtered air, ambient air, purifiednitrogen, and purified hydrogen.

In an embodiment, the gas sampling trap has a capture efficiency for thesulfurous species of at least 90%.

In an embodiment, the first stage and the second stage are providedwithin a single housing.

In an embodiment, the gas sampling trap includes an outlet provided inthe second stage and a flow path that extends from the inlet to theoutlet. The flow path is configured to direct the flow of the gasthrough the first stage and the second stage in series and to direct theacidic gas produced in the first stage into the second stage.

In an embodiment, the gas sampling trap includes a first housing, asecond housing, and a passageway that fluidly connects the first housingto the second housing. The first housing contains the first stage andincludes an intermediate outlet. The second housing contains the secondstage and includes an intermediate inlet. The passageway extends fromthe intermediate outlet to the intermediate inlet.

In an embodiment, a method is directed to sampling a gas utilizing a gassampling trap that includes a first stage and a second stage with anadsorbent substrate. The method includes directing a flow of the gasthrough the first stage and the second stage in series. This directingof the flow of the gas includes directing the gas onto a metal saltwithin the first stage to react the metal salt with a sulfurous speciesin the gas to produce acidic gas. The directing of the flow of the gasalso includes directing the acidic gas from the first stage into thesecond stage and adsorbing the acidic gas flowing through the secondstage with the adsorbent substrate.

In an embodiment, the adsorbent substrate is a porous polymer membrane.The adsorbing of the acidic gas flowing through the second stageincludes trapping the acidic gas within the porous polymer membrane.

In an embodiment, a method is directed to detecting a concentration ofsulfurous species in a gas. The method includes the sampling of the gasutilizing the gas sampling trap, disconnecting the gas sampling trapfrom a sampling manifold, and directing a solvent through the secondstage to desorb the adsorbed acidic gas from the adsorbent substrateinto the solvent. The method also includes testing the solventcontaining the desorbed acidic gas with ion chromatography to determinethe concentration of the sulfurous species in the gas.

DRAWINGS

FIG. 1 is a top view of an embodiment of a gas sampling system.

FIG. 2 is a top view of a gas sampling trap of the gas sampling systemin FIG. 1, according to an embodiment.

FIG. 3 is a longitudinal cross-sectional view of the gas sampling trapin FIG. 2, according to embodiment.

FIG. 4 is a longitudinal cross-sectional view of an embodiment of a gassampling trap.

FIG. 5 is a block flow diagram of a method of detecting a concentrationof sulfurous species in a gas.

Like numbers represent like features.

DETAILED DESCRIPTION

This disclosure is directed to sampling of gas for contaminant. Inparticular, this disclosure relates to gas traps used in sampling gas todetect for contaminant. For example, gas sampling traps herein areconfigured to sample for airborne micro-contaminants in a gas.

FIG. 1 is a top view of a gas sampling system 1. The gas sampling system1 includes a sampling manifold and a plurality of gas sampling traps 20,22, 24, 30. The gas sampling system 1 can sample for one or morecontaminants in a gas stream. The sampling manifold has a manifold inlet12 and a manifold outlet 14, and gas flows through the sampling manifoldfrom the manifold inlet 12 to the manifold outlet 14. The gas to besampled F₁ is supplied to the manifold inlet 12. The gas F₁ flowsthrough the gas sampling system 1 and is discharged from the outlet 14.Dotted arrows are provided in the Figures to illustrate the flow of gas.For example, FIG. 1 includes dotted arrows to illustrate the flow of thegas F₁ through the gas sampling system 1. The gas sampling traps 20, 22,24, 30 are connected in parallel within the sampling manifold. The gasF₁ flows through the gas sampling traps 20, 22, 24, 30 in parallel as itflows from through the sampling manifold from the manifold inlet 12 tothe manifold outlet 14. For example, a respective portion of the gas F₁is directed to flow through each gas sampling trap 20, 22, 24, 30.

The gas sampling traps 20, 22, 24, 30 can sample for various componentsin the gas F₁. The gas sampling trap 30 is configured to sample forsulfurous species in the gas F₁, as discussed in more detail below. Thegas sampling traps 20, 22, 24, 30 are configured to be non-destructiblydisconnectable (e.g., unscrewed, etc.) from the sampling manifold. Forexample, this allows for easy removal of a gas sampling trap for testingof its contents. In the illustrated embodiment, the gas sampling system1 includes four gas sampling traps 20, 22, 24, 30. However, it should beappreciated that the gas sampling system 1 in other embodiments may haveone or more gas sampling traps. In some embodiments, the gas samplingtrap 30 may be employed without the sampling manifold. For example, thegas sampling trap 30 may be directly connected to a gas source (notshown) without a sampling manifold.

FIG. 2 is a top view of the sample trap 30, according to an embodiment.The sampling trap 30 includes an inlet 32 and an outlet 34. Gas flowsthrough the sampling trap 30 by entering through the inlet 32 andexiting through the outlet 34. A flow of the gas to be sampled F₁ by thesampling trap 30 (which can be referred to as the “sample gas”) issupplied to the inlet 32 of the sampling trap 30. For example, thesampling manifold provides the flow of the sample gas F₁ to the inlet 32of the sampling trap 30.

FIG. 3 is a longitudinal cross-sectional view of the sample trap 30,according to an embodiment. The cross-sectional view in FIG. 3 is alongthe line III-III indicated in FIG. 2. The sampling trap 30 is amultistage sample trap. As shown in FIG. 3, the sampling trap 30includes a first stage 50 and a second stage 70. The first stage 50 andthe second stage 70 are fluidly connected in series. The sampling trap30 has a flow path 36 that extends from the inlet 32 to the outlet 34.The sample gas F₁ flows through the sampling trap 30 by flowing from itsinlet 32 to its outlet 34 through the flow path 36. The flow path 36directs the flow of sample gas F₁ from the inlet 32 through the firststage 50, from the first stage 50 to the second stage 70, and throughthe second stage 70 to the outlet 34.

In the illustrated embodiment, the sampling trap 30 includes a firsthousing 52 that contains the first stage 50 and a second housing 72 thatcontains the second stage 70. The housings 52, 72 can be made of arigid, chemically inert polymer such as polyether ether ketone (PEEK),ultrahigh molecular weight polyethylene (UHMWPE), and the like.

As shown in FIG. 3, the first stage 50 includes the first housing 52,and the second stage 70 includes the second housing 72. The samplingtrap 30 includes an intermediate outlet 38 and an intermediate inlet 40disposed between the inlet 32 and the outlet 34 in the flow path 36. Thefirst stage 50 includes the inlet 32 and the intermediate outlet 38(e.g., the first housing 52 includes the inlet 32 and the intermediateoutlet 38). The second stage 70 includes the intermediate inlet 40 andthe outlet 34 (e.g., the second housing 72 includes the intermediateinlet 40 and the outlet 34). The sampling trap 30 includes a passageway42 that connects the first housing 52 to the second housing 72. Thepassageway 42 extends from the intermediate outlet 38 to theintermediate inlet 40 (e.g., directly attaching the intermediate outlet38 to the intermediate outlet 40). The passageway 42 may be a separatepiece from the first and second housings 52, 72 or integral to one orboth of the first and second housings 52,72.

The first stage 50 contains a metal salt. The first stage 50 includes asubstrate 54 with the metal salt. The sample gas F₁ contacts the metalsalt as it flows through the first stage 50. The metal salt isconfigured to react with sulfurous species in the sample gas F₁ toproduce acidic gas. In an embodiment, the acidic gas is a water-solubleorganic acid. The acidic gas produced by the reaction of the metal saltand the sulfurous species can include, for example, one or more ofnitric acid and acetic acid. The term “sulfurous species” can refer to asingle sulfur-containing compound or to a plurality of sulfur-containingcompounds. The sulfurous species in the sample gas F₁ is/are gaseous.

In particular, the metal salt is configured to react with reactivesulfurous species present in the sample gas F₁. For example, suchsulfurous species can include one or more of hydrogen sulfide (H₂S),dimethyl sulfide ((CH₃)₂S), dimethyl disulfide (CH₃SSCH₃), methylmercaptan (CH₃SH), and a methyl sulfide compound (RSCH₃). In anembodiment, the methyl sulfide compound is a gaseous methyl sulfidecompound. The gaseous methyl sulfide compound includes compounds inwhich the R group is an alkyl group. In an embodiment, sulfurous speciesinclude one or more of hydrogen sulfide, dimethyl sulfide, dimethyldisulfide, and methyl mercaptan. Reactive sulfurous species do notinclude stable sulfurous species which are generally considered in theart to be chemically inert. Examples of stable gaseous sulfurous species(i.e., gaseous sulfurous species that are not reactive sulfurousspecies) include sulfur dioxide (SO₂), sulfur hexafluoride (SF₆), andthe like.

The metal salt is configured to react with sulfurous species present inthe sample gas F₁ to produce the acidic gas and a metallic sulfurcompound. The metal salt can include, for example, one or more of silvernitrate, zinc acetate, and copper acetate. The metallic sulfur compoundis a by-product of producing the acidic gas. In an embodiment, themetallic compound is a solid metallic compound formed on the substrate54. The following Equation (I) is an example of one embodiment of theacidic gas producing reaction.

2AgNO₃(s)+H₂S(g)→Ag₂S(s)+2HNO₃(g)  (I)

In the illustrated embodiment, the substrate 54 is a coated porouspolymer membrane. The polymer membrane can be made of a rigid polymermaterial such as sintered high density polyethylene (HDPE), sinteredpolytetrafluoroethylene (PTFE), and the like. The metal salt is providedon the surfaces of the porous membrane (e.g., the surfaces of the poresof the porous membrane). In an embodiment, a solution of the metal saltand a solvent (e.g., non-polar solvent, water, etc.) is applied to thepolymer membrane material and dried. The solvent evaporates forming acoating of the metal salt on the surfaces of the polymer membranematerial (e.g., external surfaces of the membrane, internal poresurfaces of the membrane). As shown in FIG. 3, the sample gas F₁ flowsthrough the porous substrate 54 as it flows through the first stage 50.For example, the sample gas F₁ contacts the metal salt as it flowsthrough the pores of the porous coated membrane. In another embodiment,the substrate 54 may be in the form of coated powder or coated granules.For example, the coated powder/coated granules can be formed of inertparticles/granules (e.g., HDPE powder/granules, PTFE powder/granules,silica gel, etc.) that are coated with the metal salt.

The mixture of the acidic gas F₂ and remaining sample gas F₃ (e.g., thesample gas F₁ minus the consumed sulfurous species) flows out of thefirst stage 50. The acidic gas F₂ and sample gas F₃ flow from the firststage 50 to the second stage 70. As shown in FIG. 3, the second stage 70is fluidly connected to the first stage 50 such that the acidic gas F₂produced in the first stage 50 flows into the second stage 70. Theacidic gas F₂ and sample gas F₃ flow from the first housing 52 throughthe passageway 42 into the second housing 72.

The second stage 70 contains an adsorbent substrate 74. The mixture ofacidic gas and sample gas F₂, F₃ contacts the adsorbent substrate 74 asthe mixture flows through the second stage. The adsorbent substrate 74is configured to adsorb acidic gas F₂. The acidic gas F₂ is adsorbed tothe adsorbent substrate 74 as it flows through the second stage 70. Theacidic gas F₂ being adsorbed from the mixture of acidic gas F₂ andsample gas F₃ by the adsorbent substrate 74 as the mixture flows throughthe second stage 70.

The adsorbent substrate 74 is a substrate that adsorbs the acidic gasproduced in the first stage 50. In an embodiment, the adsorbentsubstrate 74 is a coated porous polymer membrane. The polymer membraneis made of a polymer material. The polymer membrane can be made of arigid polymer material such as sintered high density polyethylene(HDPE), sintered polytetrafluoroethylene (PTFE), and the like. Thepolymer material of the absorbent substrate 74 may be a hydrophobicpolymer material or a hydrophilic polymer material.

The coating can include a metal salt that attracts and adsorbs theacidic gas as it flows through the second stage 70. The metal saltattracting and adsorbing the acidic gas F₂ as it flows through the poresof the adsorbing substrate 74. The metal salt can include one or moreearth metal salts of carbonate, bicarbonate, and/or hydroxide. The metalsalt can include, for example, one or more of sodium hydroxide (NaOH),sodium bicarbonate (NaHCO₃), sodium carbonate (Na₂CO₃), potassiumhydroxide (KOH), and the like.

In an embodiment, a solution of the metal salt and solvent (e.g., anon-polar solvent) is applied to the polymer membrane material and thendried. The solvent evaporates forming a coating of the metal salt on thesurfaces of the polymer membrane material (e.g., external surfaces ofthe polymer membrane, internal pore surfaces of the polymer membrane).In another embodiment, the absorbent substrate 74 may be in the form ofcoated powder or coated granules. For example, the coated powder/coatedgranules can be formed of inert particles/granules (e.g., HDPEpowder/granules, PTFE powder/granules, silica gel, etc.) that are coatedwith the adsorbent coating (e.g., the metal salt coating, etc.).

In the illustrated embodiment, the adsorbent substrate 74 is a porousmembrane. The mixture of acidic gas and sample gas F₂, F₃ are directedthrough the porous adsorbent substrate 74. The sample gas F₃ passesthrough the adsorbent substrate 74 while the acidic gas F₂ is adsorbedwithin the adsorbent substrate 74. The acidic gas F₂ becomes trappedwithin the porous membrane. The sample gas F₃ flows through the porousadsorbent substrate 74 and then flows out of the second stage 70 (e.g.,the sample gas F₃ flows from the adsorbent substrate 74 out of thesecond housing 72 and the sampling trap 30 through the outlet 34).

The adsorbent substrate 74 is configured to adsorb the acidic gas F₂ ina stable manner. The adsorbed acidic gas F₂ remains stable for asignificantly longer period than conventional sampling that contains thereactive sulfurous species (e.g., canister sampling). For example, inconventional canister sampling, a gas sample is kept within a sealedcanister/vessel and the sulfurous species react/breakdown due to itsreactivity with trace moisture and the material(s) of thecontainer/vessel. The acidic gas F₂ remains stably adsorbed to theadsorbent substrate 74 after a period of at least 10 days. In anembodiment, the acidic gas F₂ remains stably adsorbed to the adsorbentsubstrate 74 after a period of at least 14 days. In an embodiment, theacidic gas F₂ remains stably adsorbed to the adsorbent substrate 74after a period of 21 days. In experimentation of embodiments of themultistage trap 30, the chemical adsorption between the metal saltadsorbent substrate 74 and the acidic gas F₂ has resulted in the acidicgas F₂ remaining stably adsorbed 21 days after being adsorbed. In thiscontext, “stably adsorbed” means that at least 90% of the adsorbedacidic gas remains adsorbed after storing the sealed second stage atambient temperature for the specified period of time.

The gaseous sampling trap 30 is used for detecting sulfurous speciescontaminant in a gas F₁. In an embodiment, the gaseous sampling trap 30is employed in the gas sampling system 1 to sample filtered air, ambientair, purified nitrogen, or purified hydrogen. For example, purifiednitrogen contains at least 99% nitrogen and is suitable as an inert gasfor use in semiconductor manufacturing. For example, the purifiedhydrogen contains at least 99% hydrogen and is suitable for use inhydrogen fuel cells. For example, the filtered air is air filtered tohave reduced corrosion of electronic equipment in data centers andcontrol rooms (e.g., clean dry air, etc.).

The gas sampling trap 30 is configured to sample gas F₁ that containsless than 1 part per million of sulfurous species. In some embodiments,gas sampling trap 30 is configured to sample gas F₁ that contains lessthan 400 parts per billion of the sulfurous species, such as less than100 parts per billion. In an embodiment, the gas sampling trap 30 isconfigured to sample gas F₁ that contains less than 10 parts per billionof the sulfurous species. In an embodiment, the gas sampling trap 30 isconfigured to sample gas F₁ that contains less than 10 parts per billionof the sulfurous species. During testing, embodiments of the gassampling trap 30 were effective in detecting sulfurous species down to100 parts per trillion. Parts per a million/billion/trillion asdiscussed herein is in volume to volume (e.g., volume of sulfurous pervolume of the sampled gas). In some embodiments, a gas sampling trap 30can be configured to accommodate for greater concentrations of sulfurousspecies (e.g., by adjusting the sampling time accordingly, concentrationof metal salt, etc.).

FIG. 4 is a cross-section of another embodiment of a sampling trap. Theillustrated cross-section of the sampling trap 130 is a lengthwisebi-section of a sampling trap similar to the cross-section illustratedin FIG. 3 of sampling trap 30. The sampling trap 130 is a multistagesampling trap for sulfurous species. The sampling trap 130 is used formeasuring the concentration of reactive sulfurous species in a samplegas similar to the sampling trap 30 in FIGS. 1-3. In an embodiment, thesampling trap 130 is employed in a gas sampling system (e.g., gassampling system 1). The sampling trap 130 may be connected into thesampling manifold of the gas sampling system (e.g., sampling manifold).In an embodiment, the sampling trap 130 may be used instead of thesampling trap 30 in the gas sampling system 1 of FIG. 1.

As shown in FIG. 4, the sampling trap 130 includes an inlet 132, anoutlet 134, a first stage 150, and a second stage 170. The sampling trap130 generally functions in a similar manner to the sampling trap 30 inFIG. 3. For example, a flow of sample gas F₁ is supplied to the inlet132 of the sampling trap 130, flows through the sampling trap 132 byflowing through the first stage 150 and the second stage 170 in series,and then out of the sampling trap 130 through the outlet 134. The firststage 150 and the second stage 170 of the sampling trap 130 function ina manner similar as described above for the first stage 50 and thesecond stage 70 of the sampling trap 30 in FIG. 3. The first stage 150contains a metal salt (e.g., included in the substrate 154 of the firststage 150) that reacts with sulfurous species in the sample gas F₁ toproduce acidic gas F₂. The mixture of produced acidic gas F₂ and thesample gas F₃ (e.g., the sample gas F₁ minus the consumed sulfurousspecies) flow into the second stage 170, and the acidic gas is adsorbedby an adsorbent substrate 174 in the second stage 170. The metal salt,substrate 154, and adsorbent substrate 174 in the sampling trap 130 canhave similar features as discussed above for the metal salt, substrate54, and the adsorbent substrate 74 of the sampling trap 30.

As shown in FIG. 4, the sampling trap 130 includes a single housing 136.First stage 150 and the second stage 170 are provided within the singlehousing 136. The metal salt (e.g., the substrate 154 with the metalsalt) and the adsorbent substrate 174 are contained within the samehousing 136. Within the housing 136, the metal salt substrate 154 isdisposed between the inlet 132 of the housing 136 and the adsorbentsubstrate 174, and the adsorbent substrate 154 is disposed between themetal salt (e.g., the substrate 154 with the metal salt) and the outlet134 of the housing 136. In the flow path of the sampling trap 130, themetal salt (e.g., the substrate 154 with the metal salt) and theadsorbent substrate 174 are downstream of the inlet 132, and theadsorbent substrate 174 is downstream of the metal salt such that theacidic gas produced in the first stage 150 flows into the second stage170. For example, the flow of sample gas F₁, F₃ through the samplingtrap 130 causes the acidic gas F₂ produced at the metal salt substrate154 to flow to the adsorbent substrate 174 in the second stage 170.

FIG. 5 shows a block flow diagram of a method 1000 of detecting aconcentration of sulfurous species within a gas. The method starts at1100. At 1100, a gas (e.g., sample gas F₁) is sampled with a gassampling trap. For example, the gas sampling at 1100 may utilize the gassampling trap 30 in FIGS. 1-3 or the gas sampling trap 130 in FIG. 4.The gas sampling at 1110 can employ the gas sampling trap to sample thegas in a sampling manifold (e.g., sampling manifold 10). The gas issampled by the gas sampling trap at 1110 for an amount of time (e.g.,one shift, 6 hours, 8 hours, etc.). The gas sampling trap includes afirst stage (e.g., first stage 50, first stage 150) and a second stage(e.g., second stage 70, 170).

The gas sampling at 1100 can include directing a flow of the gas throughthe first stage and the second stage in series 1110. The directing ofthe flow of the gas at 1110 includes 1112, 1114, and 1116. The directingof the flow of the gas 1110 starts at 1112. At 1112, the gas is directedonto a metal salt within the first stage to react the metal salt with asulfurous species contained in the gas to produce acidic gas (e.g.,acidic gas F₂). In an embodiment, the second stage may include asubstrate with the metal salt (e.g., substrate 54, substrate 154), anddirecting the gas onto the metal salt 1112 can include directing the gasthrough the substrate (e.g., through a metal salt coated polymermembrane). The method 1000 then proceeds to 1114.

At 1114, the acidic gas produced in the first stage is directed to thesecond stage. The method 1000 then proceeds to 1116.

At 1116, the acidic gas flowing through the second stage is adsorbed byan adsorbent substrate (e.g., adsorbent substrate 74, adsorbentsubstrate 174) contained in the second stage. In an embodiment, theadsorbent substrate is a porous polymer membrane and the adsorption ofthe acidic gas at 1116 can include trapping the acidic gas within thepolymer membrane. The method 1100 the proceeds to 1200.

At 1200, the sampling trap is disconnected. In an embodiment,disconnecting the sampling trap 1200 includes disconnecting the samplingtrap from the sampling manifold (e.g., sampling manifold). In anotherembodiment, disconnecting the sampling trap 1200 includes disconnectingthe sampling manifold 1200 from a gas source (e.g., disconnecting themanifold inlet 12 and the manifold outlet 14 from a gas source). Inanother embodiment, disconnecting the sampling trap 1200 includesdisconnecting the sampling trap from a gas source (e.g., disconnectingthe inlet 32 and the outlet 34 of the sampling trap from a gas source).The disconnected sampling trap or disconnected sampling manifold (whichincludes the sampling trap) can then be transported to an off-sitetesting facility such as a testing lab. Disconnecting the sampling trap1200 can include sealing the inlet and outlet of the disconnectedsampling trap or disconnected sampling manifold (e.g., capping the inlet32 and the outlet 34, capping the manifold inlet 12 and the manifoldoutlet 14). For example, this can prevent contamination of the samplingtrap during transport. In an embodiment, the steps after 1200 areperformed off-site from the location at which the sampling 1100 occurs.The method 1000 then proceeds to 1300.

At 1300, a solvent is directed through the second stage. For example,the solvent is passed through the porous adsorbent substrate disposed inthe second stage. The adsorbent substrate is configured to adsorb theacidic gas in a manner that allows for solvent to desorb the adsorbedacidic gas. The solvent can include a liquid polar solvent (e.g., water,methanol, etc.) that desorbs the adsorbed acidic gas from the adsorbentsubstrate. For example, the solvent disrupts the adsorption/attractionbetween the adsorbed acidic acid and the adsorbent substrate. Afterbeing directed through the second stage, the solvent contains thedesorbed acidic gas. For example, the desorbed acidic gas is a liquid(e.g., liquid acetic acid, liquid nitric acid, etc.) and is contained inthe solvent by mixing with the solvent. The method 1000 then proceeds to1400.

At 1400, the solvent containing the desorbed acidic gas is tested withion chromatography to determine a concentration of the sulfurous speciesin the sampled gas. Testing the solvent containing the desorbed acidicacid with ion chromatography at 1400 includes testing the solvent withion chromatography to determine the amount of the desorbed acidic gascontained in the solvent (e.g., concentration of desorbed acidic acid inthe solvent×total amount of solvent). The amount of desorbed acidic gasin the solvent corresponds with the amount of acidic gas adsorbed by theadsorbent substrate at 1116 (e.g., the amount of desorbed acidic gas=theamount of acidic acid adsorbed by the adsorbent substrate). The amountof adsorbed acidic gas can be used to calculate the total amount of thesulfurous species consumed from the sampled gas (e.g., 1 mol of thesulfurous species produces 1 mol of the acidic gas, etc.). Theconcentration of the sulfurous species in the sampled gas can becalculated based on the total amount of consumed sulfurous species andknown volume of the gas sampled at 1100 (e.g., amount of the consumedsulfurous species/amount of the gas sampled, volume of the consumedsulfurous species/volume of the gas sampled). For example, the volume ofthe gas sampled at 1100 is known based on being documented, havingstandardized sampling conditions (e.g., standard sampling time, flowrate, pressure, etc.), or the sampling conditions being documented.

The stability of the adsorbed acidic gas permits longer times betweenthe sampling at 1100 and the testing of the sampling trap at 1300 and1400 without a significant loss in accuracy. For example, the stabilityallows for situations in which it takes longer to transport the samplingtrap from the sampling location to a testing facility (e.g.,international shipping, non-expedited shipping, shipping delays, etc.).International shipping of a sampling trap can routinely can more than 10days and can take longer than 14 days in many situations.

Capture efficiency (CE) of a sampling trap can be determined usingEquation (II):

$\begin{matrix}{{CE} = \left( \frac{\begin{matrix}{{Expected}{Sulfurous}{Species}{Concentration}{based}} \\{{on}{Measured}{Absorbed}{Acidic}{Gas}}\end{matrix}}{{Known}{Concentration}{of}{Sulfurous}{Species}{in}{Gas}{Sample}} \right)} & ({II})\end{matrix}$

For example, the “expected sulfurous species concentration based onmeasured adsorbed acidic gas” in Equation (II) can be the amount ofabsorbed acidic gas as measured by ion chromatography withchemo-luminescence. The “known concentration of sulfurous species in gassample” in Formula (II) can be measured gravimetrically. Alternatively,capture efficiency may also be determined using Equation (III):

${{Capture}{Efficiency}}{({CE}) = {\left( {1 - \frac{{Conc}{of}{sulfurous}{species}_{Downstream}}{{Conc}{of}{sulfuorous}{species}_{Upstream}}} \right) \times 100(\%)}}$

Capture efficiency measures the performance of a sampling trap andcompares the amount of sulfurous species captured by the trap relativeto the amount in the gas stream that passes through the trap. Forexample, the sampling trap 30 has been found to have an initial captureefficiency of at least 90%, at least 91%, at least 92%, at least 93%, atleast 94%, or at least 95%. In testing, embodiments of the multistagesampling trap 30 had an initial capture efficiency of at least 93.3%.Tested embodiments of the multistage sampling trap 30 utilized a silvernitrate coated porous membrane or a silver nitrate coated silica gel forthe substrate 54 in the first stage 50 and a sodium hydroxide orpotassium hydroxide coated hydrophobic membrane for the adsorbentsubstrate 74.

Sample traps have a finite capacity, which relates to how many hours thesample trap is capable of sampling, and capture efficiency graduallydecreases over time as the sample trap captures the contaminants. Forthis reason, the capacity of a sample trap is often defined at aparticular capture efficiency, which serves as a practical operatinglimit. More specifically, capacity is defined as the absolute amount byweight of contaminant (i.e., the sulfurous species) that a sample trapcan hold and has typical units of parts per billion hours (ppb-hrs)—theproduct of time and challenge concentration. Capacity can depend on, forexample, concentration, flow, temperature, and relative humidity, andmay further depend on the chemical or physical interaction between thecontaminant and the sample trap medium, such as the treatmentconcentration. Typically, capacity is defined at a particular captureefficiency. For example, the sample traps disclosed herein have beenfound to have a capacity of at least 100 ppb-hr at 90% captureefficiency, such as at least 150 ppb-hrs, at least 200 ppb-hrs, or atleast about 250 ppb-hrs at 90% capture efficiency.

As specific examples, a gaseous stream having a known concentration ofhydrogen sulfide (H₂S) was introduced into the inlet of the housing of asample trap in which a silver nitrate treated porous frit was inserted.The hydrogen sulfide gas stream was allowed to pass from the inlet ofthe housing through the treated frit where a reaction occurred with thesilver nitrate to produce a silver sulfide effluent. The effluent thenexited the outlet of the housing, and the outlet sulfur concentrationwas recorded every fifteen minutes. The capacity was then calculatedusing Equation (III). Results are shown in Table 1 below.

TABLE 1 Sample Trap 1 Sample Trap 2 Sample Trap 3 0.1M AgNO₃ 0.1M AgNO₃0.5M AgNO₃ <10% RH 45% RH <10% RH 100 100 250Capacity values were recorded at 9-% capture efficiency (ppb-hrs). Asthe data shows, the capacity of the sample trap was found to beindependent of the relative humidity of the gas stream (measured using acalibrated hydrometer). However, the higher the silver nitratetreatment, the higher the sample trap capacity.

The accuracy and precision of sulfurous gas concentration valuesrelative to the actual concentration values were also determined. Inthis example, known concentrations of hydrogen sulfide were generatedand passed through sample traps that included a silver nitrate treatedporous frit. The resulting effluent was then measured by IonChromatography. The average calculated hydrogen sulfide values(ppb-volume) were then compared to the known values. The results areshown in Table 2.

TABLE 2 Known Conc Measured Conc (ppb-V) Margin of Error Uncertainty@99% (ppb-V) Ave Accuracy Precision RPD (%) @99% (ppb-V) 1.4 1.4 97%0.09 7.0 6.6 0.3 2.9 3.0 105%  0.2 5.1 6.2 0.8 6.6 6.3 96% 0.4 5.9 6.51.9 17 15 93% 0.3 1.9 2.0 1.4 29 30 101%  1.1 3.7 4.3 5.4 67 63 93% 1.52.4 2.6 7.5

Aspects:

Any of Aspects 1-13 can be combined with any of Aspects 14-20.

Aspect 1. A gas sampling trap, comprising: a first stage including aninlet for receiving a flow of gas, the first stage containing a metalsalt configured to react with sulfurous species contained in the gas toproduce an acidic gas; and a second stage fluidly connected to the firststage such that the acidic gas produced in the first stage flows intothe second stage, the second stage containing an adsorbent substrateconfigured to adsorb the acidic gas flowing through the second stage.

Aspect 2. The gas sampling trap of Aspect 1, wherein the reaction of themetal salt with the sulfurous species produces the acidic gas and ametallic sulfur compound.

Aspect 3. The gas sampling trap of either one of Aspects 1 or 2, whereinthe metal salt includes one or more of silver nitrate, zinc acetate, andcopper acetate.

Aspect 4. The gas sampling trap of any one of Aspects 1-3, wherein thesulfurous species includes one or more of hydrogen sulfide, dimethylsulfide, dimethyl disulfide, methyl mercaptan, and a methyl sulfidecompound.

Aspect 5. The gas sampling trap of any one of Aspects 1-4, wherein theacidic gas includes one or more of nitric acid and acetic acid.

Aspect 6. The gas sampling trap of any one of Aspects 1-5, wherein theadsorbent substrate adsorbs the acidic gas such that the acidic gasremains stably adsorbed to the adsorbent substrate after a period of 10days.

Aspect 7. The gas sampling trap of any one of Aspects 1-6, wherein theadsorbent substrate is a porous polymer membrane that adsorbs the acidicgas such that the acidic gas is trapped within the porous polymermembrane.

Aspect 8. The gas sampling trap of any one of Aspects 1-7, wherein thegas contains less than 400 parts per billion of the sulfurous species.

Aspect 9. The gas sampling trap of any one of Aspects 1-8, wherein thegas is one of filtered air, ambient air, purified nitrogen, and purifiedhydrogen.

Aspect 10. The gas sampling trap of any one of Aspects 1-9, wherein thegas sampling trap has an initial capture efficiency for the sulfurousspecies of at least 90%.

Aspect 11. The gas sampling trap of Aspect 10, wherein the gas samplingtrap has a capacity of at least 100 ppb-hr at a capture efficiency of90%.

Aspect 12. The gas sampling trap of any one of Aspects 1-10, wherein thefirst stage and the second stage are provided within a single housing.

Aspect 13. The gas sampling trap of any one of Aspects 1-11, furthercomprising: an outlet provided in the second stage; and a flow pathextending from the inlet to the outlet, the flow path configured todirect the flow of the gas through the first stage and the second stagein series and to direct the acidic gas produced in the first stage intothe second stage.

Aspect 14. The gas sampling trap of any one of Aspects 1-10 and 12,comprising: a first housing containing the first stage, the firsthousing including an intermediate outlet; a second housing containingthe second stage, the second housing including an intermediate inlet;and a passageway fluidly connecting the first housing to the secondhousing, the passageway extending from the intermediate outlet to theintermediate inlet.

Aspect 15. A method of sampling a gas utilizing a gas sampling trap, thegas sampling trap including a first stage and a second stage, the methodcomprising: directing a flow of the gas through the first stage and thesecond stage in series, wherein the directing of the flow of the gasincludes: directing the gas onto a metal salt within the first stage toreact the metal salt with a sulfurous species contained in the gas toproduce acidic gas, directing the acidic gas from the first stage intothe second stage, and adsorbing, with an adsorbent substrate containedin the second stage, the acidic gas flowing through the second stage.

Aspect 16. The method of Aspect 14, wherein the metal salt includes oneor more of silver nitrate, zinc acetate, and copper acetate.

Aspect 17. The method of either one of Aspects 14 and 15, wherein theacidic gas includes one or more of nitric acid and acetic acid.

Aspect 18. The method of any one of Aspects 14-16, wherein the sulfurousspecies includes one or more of hydrogen sulfide, dimethyl sulfide,dimethyl disulfide, methyl mercaptan, and a methyl sulfide compound.

Aspect 19. The method of any one of Aspects 14-17, wherein the adsorbentsubstrate adsorbs the acidic gas such that the acidic gas remains stablyadsorbed to the adsorbent substrate after a period of 10 days.

Aspect 20. The method of any one of Aspects 14-18, wherein the adsorbentsubstrate is a porous polymer membrane wherein the adsorbing of theacidic gas includes trapping the acidic gas within the porous polymermembrane.

Aspect 21. A method of detecting a concentration of sulfurous species ina gas, the method comprising: sampling a gas utilizing a gas samplingtrap according to the method of any one of Aspects 14-19; disconnectingthe gas sampling trap from a sampling manifold; directing a solventthrough the second stage, the solvent desorbing the acidic gas adsorbedin the adsorbent substrate into the solvent; and testing the solventcontaining the desorbed acidic gas with ion chromatography to determinea concentration of the sulfurous species in the gas.

The examples disclosed in this application are to be considered in allrespects as illustrative and not limitative. The scope of the inventionis indicated by the appended claims rather than by the foregoingdescription; and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A gas sampling trap, comprising: a first stageincluding an inlet for receiving a flow of gas, the first stagecontaining a metal salt configured to react with sulfurous speciescontained in the gas to produce an acidic gas; and a second stagefluidly connected to the first stage such that the acidic gas producedin the first stage flows into the second stage, the second stagecontaining an adsorbent substrate configured to adsorb the acidic gasflowing through the second stage.
 2. The gas sampling trap of claim 1,wherein the reaction of the metal salt with the sulfurous speciesproduces the acidic gas and a metallic sulfur compound.
 3. The gassampling trap of claim 1, wherein the metal salt includes one or more ofsilver nitrate, zinc acetate, and copper acetate.
 4. The gas samplingtrap of claim 1, wherein the sulfurous species includes one or more ofhydrogen sulfide, dimethyl sulfide, dimethyl disulfide, methylmercaptan, and a methyl sulfide compound.
 5. The gas sampling trap ofclaim 1, wherein the acidic gas includes one or more of nitric acid andacetic acid.
 6. The gas sampling trap of claim 1, wherein the adsorbentsubstrate adsorbs the acidic gas such that the acidic gas remains stablyadsorbed to the adsorbent substrate after a period of 10 days.
 7. Thegas sampling trap of claim 1, wherein the adsorbent substrate is aporous polymer membrane that adsorbs the acidic gas such that the acidicgas is trapped within the porous polymer membrane.
 8. The gas samplingtrap of claim 1, wherein the gas contains less than 400 parts perbillion of the sulfurous species.
 9. The gas sampling trap of claim 1,wherein the gas is one of filtered air, ambient air, purified nitrogen,and purified hydrogen.
 10. The gas sampling trap of claim 1, wherein thegas sampling trap has an initial capture efficiency for the sulfurousspecies of at least 90%.
 11. The gas sampling trap of claim 10, whereinthe gas sampling trap has a capacity of at least 100 ppb-hr at a captureefficiency of 90%.
 12. The gas sampling trap of claim 1, wherein thefirst stage and the second stage are provided within a single housing.13. The gas sampling trap of claim 1, further comprising: an outletprovided in the second stage; and a flow path extending from the inletto the outlet, the flow path configured to direct the flow of the gasthrough the first stage and the second stage in series and to direct theacidic gas produced in the first stage into the second stage.
 14. Thegas sampling trap of claim 1, comprising: a first housing containing thefirst stage, the first housing including an intermediate outlet; asecond housing containing the second stage, the second housing includingan intermediate inlet; and a passageway fluidly connecting the firsthousing to the second housing, the passageway extending from theintermediate outlet to the intermediate inlet.
 15. A method of samplinga gas utilizing a gas sampling trap, the gas sampling trap including afirst stage and a second stage, the method comprising: directing a flowof the gas through the first stage and the second stage in series,wherein the directing of the flow of the gas includes: directing the gasonto a metal salt within the first stage to react the metal salt with asulfurous species contained in the gas to produce acidic gas, directingthe acidic gas from the first stage into the second stage, andadsorbing, with an adsorbent substrate contained in the second stage,the acidic gas flowing through the second stage.
 16. The method of claim14, wherein the metal salt includes one or more of silver nitrate, zincacetate, and copper acetate.
 17. The method of claim 14, wherein theacidic gas includes one or more of nitric acid and acetic acid.
 18. Themethod of claim 14, wherein the sulfurous species includes one or moreof hydrogen sulfide, dimethyl sulfide, dimethyl disulfide, methylmercaptan, and a methyl sulfide compound.
 19. The method of claim 14,wherein the adsorbent substrate adsorbs the acidic gas such that theacidic gas remains stably adsorbed to the adsorbent substrate after aperiod of 10 days.
 20. The method of claim 14, wherein the adsorbentsubstrate is a porous polymer membrane wherein the adsorbing of theacidic gas includes trapping the acidic gas within the porous polymermembrane.
 21. A method of detecting a concentration of sulfurous speciesin a gas, the method comprising: sampling a gas utilizing a gas samplingtrap according to the method of claim 14; disconnecting the gas samplingtrap; directing a solvent through the second stage, the solventdesorbing the acidic gas adsorbed in the adsorbent substrate into thesolvent; and testing the solvent containing the desorbed acidic gas withion chromatography to determine a concentration of the sulfurous speciesin the gas.